5b. Heads and Valve Gear
Later Series 'C' head with web.
The rear head looked to be in very good original condition, with the exhaust and spark plug threads almost perfect and the tolerance's of the rocker tunnels and upper valve guides still ok.
The front head looked to have had much remedial work already carried out on it to restore these common faults, but the good news was that the work looked to have been very professionally carried out.
|Brass (bronze?) inserts had been
applied in 3 areas, one to restore the exhaust thread, one to restore the
thread of one of the rocker cap threads and another to restore the internal
bore of one of the rocker tunnels.
This latter problem is quite common, it resulting from the aluminium rocker pin bearing moving in the tunnel when the head heats up. Once this movement starts, it does not take too long for the bore to wear to a point where the whole rocker is wobbling in the tunnel (note : to get round this, a later design of oil feed bolts can now be purchased that lock the rocker bearing in the tunnel).
Both heads had also had new valve seats inserted, again this work seemed to have been professionally carried out. It was fair to say then, that as bought both heads looked to be in good condition, ready for any tuning work I wanted to carry out.
Next step was to have the inlet tracts bored out to 32mm and then the heads gas-flowed. In the past with Norton ES2's, I had found that opening the inlet tract had had the single most radical effect on power, allowing the engine to breath far better.
I did not know much about boring the inlet tracts of Vincent heads when I bought the bike, however, the previous owner told me that it was actually possible to bore a rear head out to 32mm, providing you were very careful!
|Luckily, he recommended to me a
well known gas flow expert in Coventry called Les Ryder, who had sucessfully
carried out this work many times before.
I went out to meet Les at his home, where he had a small workshop at the back, from which he did all his work. I left the heads with him, in good company as sate around the shed was everything ranging from a Manx Norton head to a modern Kawasaki drag engine head.
Over the next year I visited him a number of times, finding him to be not only a brilliant head tuner but a real gentleman as well. He told me about some of his exploits in the second world war, in which amazingly enough he had participated as a horse mounted cavalryman in 1939, later moving on to Bren Carriers.
Both tracts were successfully bored out to 32mm, but unfortunately it turned out that on one of the heads, the inlet guide hole was slightly out of line, resulting in it being impossible to get a good valve seat cut.
|The only option available was to
remove the lower (phoshpor bronze) guide, weld the hole up and then line
bore the hole out again, to ensure it was straight. As this job was beyond my workshop and skill, Don Alexander offered to carry it out for me and made an excellent job of it, resulting in it being
possible to re-cut a good valve seat face.
Apart from the inlet tracts being opened up and polished, the other very noticeable part of Les's flowing was to relieve the combustion chambers around the valve seats. I believe the reason for this is to aid the passage of fuel into the chamber as the inlet valve opens. The whole job was beautifully done, finished off by the chambers and tracts being highly polished.
Both heads and barrels were in bare metal when I acquired them, which was fine while I was working on them. Once all the engineering work had been completed I wanted to finish them in a nice gloss black finish, giving them that famous look that was associated with their namesake. I know that some prefer the natural finish of a Rapide, but I have always thought the black version looks far more purposeful and imposing.
The dilema for me was more about what finish to use on the heads and barrels. I wanted something that would be both attractive and durable, but there are not many finishes that will withstand the heat given off by air cooled cylinder heads. In the past I had used brushed on 'Pot Black' which gives a reasonable satin finish and is able to cope with the heat, but unfortunately is not very durable. I felt that this restoration deserved something a bit better than that.
|I toyed with the idea of using Acrylic
2-pack, similar to that used on the other main engine castings, however,
I doubted it would be able to withstand the heat. I also considered using
a high gloss paint I had bought about 8 years ago that is supposedly used
on Bentley cylinder heads. I was especially keen to use this as I had bought
over a gallon of the darn stuff!, but again, as it was a brush finish I
doubted it would be durable enough.
Eventually I chickened out of doing it myself and passed it over to Bryan Dees at Deespray. Bryan is well known to Vincent Owners Club members, whose magazine he regularly advertises with, I had also heard first hand accounts complimenting his work.
Although it took Bryan some time to complete the work (I gather he is a one man band and has a lot of other work on) the results when they came back were excellent. It looks very much like a black gloss stove enamel and is a very high quality finish. Bryan also made an excellent job of masking off all the mating faces and orifices, which is very important as this can be very difficult to remove. Not only that but he delivered to my door, thanks Bryan!
When I originally bought the bike I understood that it was really the excellent main castings that I was buying, and that most of the internals would need refurbishment, including the valve gear. This was not really a problem, as in some ways it is easier to build the engine yourself with new parts, so you will know exactly what is in it.
It seems like a long time ago now (I think about 12 years), but buying the valve gear was the first large single expenditure I made after buying the bike. At that time I had been used to scrimping around at autojumbles to find new parts for my Norton's and it was nice to find such an established cottage industry in place for supplying Vincent parts.
I rang Ron Kemp in South Wales and ordered everything I would need to refurbish the heads, this included the following new parts:
|· Inlet and Exhaust valves
· Lower valve guides (ET41) and Upper valve guide Washers (ET40)
· Valve guide securing collars (screw into head to secure guides)
· Valve springs
· Upper valve spring caps (ET37) and collets (ET36/ET38)
· Valve Collars (ET35)
· Rocker Bearings (ET26). Three of the four bearings were special 'extended bearings', see below.
· Rocker Pins (ET28)
· Tappet Adjusters (ET27)
· Modified Rocker Feed Bolts (ET100). These include a lower retaining pad for securing the rocker bearings, see below.
· All washers and seals, including the large washers for the inspection caps
|As you can see from the list, there
was not a lot that I dident replace! Having sent Ron the order list, I took
a day off with Titch to visit Ron at his home in Wales and collect the parts.
As well as being a very interesting visit, for me it was a little bit like
a kid being in a candy shop!
I also took the opportunity to buy some of the rocker oil feed pipes, as Ron had some available and the ones that had come with the bike were a bit tatty, having small dents in the pipes.
Once home, all the parts were then put in a large biscuit tin where (apart from occasional visits to trial fit a valve in the heads) they remained until I came to assemble the valve gear. Fast forward 12 years . . .
|Valve Gear Assembly
By this time all work on the heads had been completed and the heads and barrels had been enameled. Given the amount of work that had been put into preparing the heads ready to accept the new valvegear, assembly was actually a bit of an anti-climax.
As part of having the seats cut, I had already fitted the lower guides. The guide arrangements for Vincent cylinder heads is very unusual, having a lower and an upper guide, which in theory, results in them running very true with little deflection. The rocker acts on a collar (ET35) that sits between the two guides. Because the lower guide has a relatively small contact patch with the cylinder head, these are retained by small screw in rings with slots in them. I had made a special tool to insert these slotted rings, which ensured that they were in fully tight, without slipping and ruining the slot. Before fitting the guides though, I had to machine the top off them, so that they would not protrude beyond the locking ring as the standard ones do. This is a necessary modification if using racing cams, else on full lift they will foul the collars (ET35).
|Assembling the valves with springs,
collars etc. was not really a problem. The ET35 collars do need some effort
to ensure they are fully home on the stepped valves, but providing the valve
head is suitably supported and a soft drift is used this is not a problem.
I had acquired a genuine set of Aero (Terry's?) Black Lightning valve springs
some years ago, but decided to stay with the set I had purchased from Ron
Kemp. The Lightning valve springs have 3 separate springs per valve, instead
of the normal 2, I assume the spring strength of the 2 main springs are
the same as standard ones, although I have not measured them. In the Vincent
part's list the 3rd spring is referred to as ET39/2 (Auxillary), although
it does not seem to be mentioned in the text.
I will see how I get on with just 2 sets to start with, as can only imagine this 3rd set being needed if holding sustained high revolutions near the rev limit. (Does anyone have any more information about these springs?).
The rockers that came with the bike were in good condition, the feet not requiring any work other than a light stoning. Black Lightning (and Shadow) rockers I believe were supplied highly polished so I carried out the same treatment on these rockers.
I also removed any excess metal from the rockers, to make them as light as possible, without weakening them to the point of possible failure. This is a very useful exercise to carry out on any racing engine, as this is reciprocal weight and reducing it can result in higher rev's with less possibility of valve bounce. That said, the amount it is possible to reduce from these rockers I found to be relatively small.
|The most common fault with Vincent heads seems
to be that the rocker bearings (ET26/1) tend to move in the head rocker
tunnels, as they are only a light press fit in. Once this movement starts
it can result in excess wear in the tunnels, which in turn makes the problem
To help alleviate this problem Ron Kemp supplies a special ET26, which had extended 'ears' so that more bearing metal will be in contact with the rocker tunnel. I purchased 3 of these bearings, there being little point in buying a fourth, as one of the tunnels had been re-sleeved only the length of a standard bearing. (see photograph).
|In addition to the extended rocker
bearings, the other way to help prevent the bearings moving is to use a
modified oil feed bolt (ET100). While a standard ET100 would screw into
the head itself, this modified version has a thread at its end and is used
in conjunction with a special threaded retainer plate that slots between
the rocker bearing and the rocker (this can just be seen protruding in the leftmost rocker, above). The modified ET100 now passes straight through the head casting and screws into
the retaining plate, it in turn tightens the rocker bearing against the
The only problem with using these though, was that the threaded retaining plates had been made slightly oversize and would not fit between the bearings and rockers. Again, my lathe proved invaluable, and I was able to machine each plate to the correct size.
|The rocker pins (ET28) are a press
fit into the rockers, while moving freely on the rocker bearings. To facilitate
this I used my bench press to assemble. As is often the case, things did
not go completely according to plan and I found that 3 of the 4 rockers
had some tightness after assembly. This seemed strange as the components
seemed a good fit before the pin was inserted. On closer inspection I found
that the rocker bearings needed very slight easing with a fine file and
the side faces of the rockers needed slight stoning to remove all traces
of burrs. With this work done, on re-assembling, each rocker now moved beautifully,
with no signs of stiffness.
Final job was to insert the completed rocker/bearing assembly into the rocker tunnels. This, predictably, was a very fiddly job, taking considerable time and cussing to get them all in place. I'm sure the more experienced Vincent enthusiasts out there, on reading this will be laughing at my inaptitude at this task, but I still not sure if there is any way of completing this task without much use of four letter words!
Once the bearings were inserted I then screwed in the modified ET100 oil feed bolts, which completed the head assembly.
|I am pleased to report that the rockers look to move freely and without fouling the valve stems, which I gather is quite important. It being over 12 years ago that I first started work on the heads, I was certainly glad to see them finished.|
Valve Inspection Caps